In recent years, communication security techniques for enabling secure communication between computers have been developed along with the development of computer networks. Communication security techniques of the related art include a method using an SDK, a method using a security protocol such as HTTPS or the like, and an IP examination method. Since these communication security techniques are difficult to implement, high-quality manpower is required in building and managing a communication system. It is also time-consuming and costly to build and manage the communication system. Thus, a demand has existed for a communication security technique, which can be implemented easily and quickly.